1. Field of the Invention
The present invention generally relates to a chemical mechanical polishing (CMP) slurry and to a method of using the CMP slurry. More particularly, the present invention relates to a CMP slurry for use in polishing of an aluminum film, to a CMP method using the slurry, and to a method of forming an aluminum wiring using the CMP method.
A claim of priority is made to Korean Patent Application No. 2003-70281, filed on Oct. 9, 2003 in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.
2. Description of the Related Art
Aluminum is commonly used as the conductive material forming wirings and/or conductive plugs in semiconductor devices. Herein, the term “aluminum” is inclusive of aluminum alloys in which aluminum is the main component.
Conventionally, an aluminum wiring or the like is formed by first depositing an aluminum film by sputtering or chemical vapor deposition (CVD), and then reactive ion etching (RIE) the aluminum film to define a wiring pattern. However, this technique is not well suited to highly integrated devices having extremely small pattern widths and extremely small gaps between patterns. That is, as the pattern density increases, the likelihood of bridges formed between adjacent wiring patterns also increases. Also, voids can form in the aluminum patterns as a result of heat stress induced migration after thermal processing or electro-migration.
A so-called damascene method was thus developed in an effort to overcome the drawbacks associated with the conventional RIE technique. The damascene method generally includes depositing an inter metal dielectric (IMD) layer, patterning the IMD layer to define a metal wiring region within the IMD layer, forming a metal barrier layer on the resultant structure, depositing a thick aluminum film on the metal barrier layer, and removing the aluminum film and the metal barrier layer on an upper surface of the IMD using a CMP process.
The CMP process of the damascene method can substantially impact electrical characteristics of the aluminum wiring. For example, if the removal rate selectivity (etch selectivity) of the aluminum film to the IMD layer (typically silicon oxide) is too low, the aluminum film can be over etched in the CMP process. Over etching can decrease of the surface area of the aluminum wiring, which results in an increased electrical resistance of the aluminum wiring, which in turn can decrease the signal speed of the semiconductor device.
Examples of CMP slurries for aluminum films are disclosed in U.S. Pat. No. 5,209,816 and Japanese Laid-Open Patent No. 10-44047. However, aluminum to silicon oxide removal rate selectivity of the disclosed slurries is less than 20. As such, over etching of the aluminum wiring can result if these slurries are used in the fabrication of highly integrated devices having extremely small wiring dimensions.
Commercially available CMP slurries for aluminum films include those having product designations EP-A5680 (Cabot Co.) and CMP9003 (EKC Co.). EP-A5680 includes alumina as a polishing agent and H2O2 and (NH4)2S2O8 as oxidants, and has a pH of approximately 3.
The removal rate of an aluminum film when EP-A5680 is used as the polishing slurry deviates widely in a range of 1,500˜6000Å per minute. Also, the use of EP-A5680 can result in defects such as scratches and corrosion on the surface of the aluminum film. That is, scratch defects create a surface roughness on the aluminum film and are caused by the polishing agent contacting the surface of the aluminum film. In severe cases, the scratch defect can form a pit in the surface of the aluminum film which can adversely affect device performance. Corrosion can result when aluminum ions break away from the aluminum film by a chemical reaction with other materials. These defects are generally the result of material characteristics of aluminum, i.e., relatively low hardness and low resistance to stress. Scratches or corrosion on the aluminum film can reduce the reflective index of the aluminum film and decrease reliability of the aluminum wiring. In some cases, these defects can lead to discontinuities (open circuits) in the aluminum wiring.
The CMP9003 slurry exhibits comparatively less scratch related defects than the EP-A5680 slurry. However, aluminum to silicon oxide removal rate selectivity of the CMP9003 slurry is relatively low, which as discussed above can lead to problems when using the slurry in the fabrication of highly integrated semiconductor devices.